The present invention relates to pulse arc welding machine. More particularly, the invention relates to a method of controlling the feeding speed of a wire electrode and a welding arc current for a pulse arc welding machine.
There has been previously disclosed a conventional pulse arc welding machine as indicated in FIG. 1. In FIG. 1, reference numeral 1 designates a DC power source circuit which operates from an AC power source such as a three-phase AC power source, 2 a switch group of producing a predetermined pulse current and a pulse frequency by making or breaking the connection of the output from the DC power source circuit 1 in accordance with a control signal produced by a switch instructing circuit 3, 8 a DC reactor, 7 a flywheel diode for preventing the application of a reverse high voltage produced by the DC reactor to the output of the switch group immediately after the switch group 2 is opened, 9 an auxiliary power source for supplying a primary welding DC current (hereinafter referred to as "a base current") for maintaining a welding arc, 11 a reel on which a wire electrode is wound, 12 a consumable wire electrode, and 13 a welding torch to which the wire electrode 12 is fed by a wire feeding motor 14. A shielding gas is supplied to the welding torch 13 for shielding the welding section from the atmosphere during welding operations. Further, reference numeral 17 designates a base material to be welded, and 18 a control panel for setting input values to the switching circuit 3 including thereon a wire material selecting dial 19 for the material of the welding wire, a shielding gas selecting dial 20 for the type of the shielding gas, a welding voltage setting dial 21 for setting the optimum welding arc voltage, a welding or arc current setting dial 22 for setting the optimum welding arc current value (average arc current value) and a wire diameter selecting dial 23 for the diameter for the wire. Reference numeral 24 designates a peak current setting circuit which computes the peak value I.sub.p of pulse current from the combination of the material of the wire thus selected and the type of the shielding gas, computing a peak value instruction signal a. Reference numeral 25 designates a pulse width setting circuit which computes the pulse width .tau. of the pulse current from the welding voltage value thus set, outputting a pulse width instruction signal b, 26 a frequency setting circuit which computes a pulse frequency N.sub.0 from the welding or arc current value thus set outputting a pulse frequency instruction signal c, and 27 a function selecting circuit for selecting the relationships between the pulse frequency and the wire feeding speed from the diameter of the wire thus selected, outputting a wire feeding function signal f.sub.1 (N). 28 indicates a wire feeding speed computing circuit which computes a wire feeding speed v from the pulse frequency instruction signal c and the function signal f.sub.1 (N), outputting a wire feeding speed instruction signal d, and 29 a base current instructing circuit to which a signal e for setting a base current value I.sub.BO to be supplied from the auxiliary power source 9 is inputted.
FIG. 2 shows a welding current waveform 30 in the aforementioned conventional pulse arc welding machine during a welding operation.
The operation of the conventional pulse arc welding machine thus constructed will be described.
The material of the wire to be fed into the welding torch 13, the diameter of the wire and the type of shielding gas introduced into the welding torch are determined beforehand, and the wire material selecting dial 19 and the shielding gas selecting dial 20 are set in accordance with the selected material of the wire and type of the shielding gas. The values set with the dials 19 and 20 are applied to the inputs of the peak current setting circuit 24 which in response produces a peak value instruction signal a which is applied to one input of the switch instructing circuit 3.
Subsequently, a welding or arc current value is determined in accordance with the thickness and the like of the base material, and the welding current setting dial 22 is set in accordance with the welding current value thus predetermined. The set value from the dial 22 is applied to the input of the frequency setting circuit 26 which in response thereto produces a pulse frequency instruction signal c the value of which is set substantially in proportion to the welding or arc current. The signal c is in turn applied to both the other input c of the switch instructing circuit 3 and to one input of the wire feeding speed computing circuit 28.
Then, the wire diameter selecting dial 23 is set in accordance with the chosen diameter of the wire. The data thus selected is in turn applied to the input of the function selecting circuit 27, which consequently produces a corresponding selected function signal f.sub.1 (N) which is in turn applied to the other input of the computing circuit 28.
After the wire feeding speed computing circuit 28 has received both the pulse frequency instruction signal c and the function signal f.sub.1 (N), the computing circuit 28 sequentially produces a wire feeding speed instruction signal d which is applied to the input of the wire feeding motor 14.
Thereafter, a welding or arc voltage capable of providing an optimum welding bead under given welding conditions is effectively selected and the welding voltage setting dial 21 is set in accordance with the welding or arc voltage value thus determined. The value set by the dial 21 is applied to the input of the pulse width setting circuit 25 which sequentially produces an instruction signal b corresponding to the pulse width .tau., which varies substantially in proportion to the welding or arc voltage value which is applied to another input of the switch instructing circuit 3.
After the signals a, b and c are supplied from the peak current setting circuit 24, the frequency setting circuit 26 and the pulse width setting circuit 25 to the switch instructing circuit 3, the switch instructing circuit 3 sets a welding or arc current. The resulting current waveform 30 having a pulse width .tau., a pulse peak current I.sub.p and a pulse frequency N.sub.0 as shown in FIG. 2.
Further, the signal d applied from the wire feeding speed computing circuit 28 to the wire feeding motor 14, as described above, sets the speed of the motor 14 and hence the wire feeding speed v.
With the welding or arc current thus set by the switch instructing circuit 3 as described above, the arc current will melt the wire electrode and accordingly weld the base material with an arc length and hence arc voltage set in such a manner that the rate of production of molten wire electrode droplets is optimized by proper setting of the wire feeding rate.
The base current I.sub.BO acts as an arc maintaining current, the requiered minimum value of which depends slightly upon the material of the wire and the diameter of the wire and the like. However, when the base current is set at the highest value such as, for instance, 20A, no readjustment of the pulse arc welding machine is necessary.
In the conventional pulse arc welding machine constructed as described above, if any one of the material of the consumable wire electrode to be welded, the diameter of the wire and the type of the shielding gas is varied, the peak current value I.sub.p, the pulse width .tau. and the wire feeding speed v of the pulse current for producing an optimum bead will vary accordingly. Therefore, the respective dials 21, 22 and 23 should be reset in accordance with the changed values of the material and the diameter of the wire electrode and the type of the shielding gas. It is of course complicated and time consuming to adjust the pulse arc welding machine for an optimum welding state in this manner each time one of these parameters is varied.